Re: Polyphase clock sync ccf symbols needed?

GNU Radio
1

On Sun, Apr 28, 2013 at 8:39 PM, Tom R. [email protected] wrote:

then

damp factor= 0.707

floor) is the number of the filterbank being used at that time, which

reducing noise bandwidth. But, steady state value of 24 reaches after

Sam

Sam,

No, I don’t think that you are doing something wrong here. But those
figures you’ve posted look like the circuit is under-damped. It should
be critically damped,

Why the circuit should be critically damped? In my first mail, I said
that
I am using damp_factor= 0.707. It should be under-damped. No? The
problem,
i think, is that its taking too long 9000/4 symbols to get lock. No ?

so it’d be interesting to see what’s going wrong

inside of the algorithm. I’ve looked at it with this in mind, but I
can’t see that anything is being done differently than the normal
control loops that we use, and the parameters should be set to be
critically damped.
This sounds like something we can develop and discuss on the signal
processing wiki page. Would you be able to start something here?
There’s already a section for Synchronization. Maybe just create a new
page off that for discussing this particular algorithm/block.

I’ll be glad to :slight_smile:

(for signing up to post on the wiki:

http://gnuradio.org/redmine/projects/gnuradio/wiki/FAQ#How-can-I-post-on-this-wiki-use-the-bug-tracker

)

Thanks!
Tom

–

Best Regards,

Sam

2

On Mon, Apr 29, 2013 at 4:10 AM, Sam mite [email protected] wrote:

Sam,

No, I don’t think that you are doing something wrong here. But those
figures you’ve posted look like the circuit is under-damped. It should
be critically damped,

Why the circuit should be critically damped? In my first mail, I said that I
am using damp_factor= 0.707. It should be under-damped. No? The problem, i
think, is that its taking too long 9000/4 symbols to get lock. No ?

Hm, it appears you’re right that it’s under damped. I thought I had
translated it so that 0.707 was crtically damped, but apparently I
didn’t. I was looking at the Costas loop implementation to make sure.
But they converges at the same time.

However, in the case of the timing loop, we’re not talking about a
slight under damping. With .707, I would expect it to dip slightly
before converging. But the way this looks, it is significantly under
damped with the number of cycles of oscillation. So I still think
something isn’t quite right. Not sure if it will necessarily converge
any faster, but it should behave more like expected.

I’ll be glad to :slight_smile:

Thanks!
Tom